Poly(alkylphenol) polysulfides, known under the name Vultac®, are vulcanizing agents that are widely used in the rubber industry as sulfur donors. This latter expression is intended to denote, in the field of rubbers, a compound (or mixture of chemical compounds) that is capable of liberating sulfur by heating at the vulcanization temperature, so as to cross-link rubbers or elastomers which contain double bonds in their main or side chain. Poly(alkylphenol) polysulfides indeed contribute both to the satisfactory progress of the vulcanization reaction and to the mechanical properties of vulcanized articles manufactured from natural rubber, synthetic rubbers of the SBR (Styrene Butadiene Rubber) type or chlorobutyl rubbers or mixtures thereof. One of their most valued advantages is that they do not possess nitrogen or an amine group, and consequently cannot generate nitrosamines or contribute to their formation.
In the field of rubber, the presence of nitrosamines has in point of fact been recognized for a long time as a serious hazard for health, both for persons who work in manufacturing units and for users or consumers who are in contact with vulcanized articles after forming. This is why the rubber industry is continually striving to eliminate or limit emissions of nitrosamines and chemical products that are capable of generating these. Rubbers of the EPDM (Ethylene Propylene Diene Monomer) type are obtained by copolymerization of ethylene, propylene and a dienic monomer. They come within the field of industrial rubbers, and are particularly used, after vulcanization, in the manufacture of profiled sections for the automobile industry or for building. These sections are widely used for their mechanical properties, their impermeability qualities and their ageing resistance. Mention may be made, for example in the automotive field, of profiled sections which provide a seal between the glass and the metal part of the door and, in the building construction field, glazing seals.
Consideration has been given to the incorporation of poly(alkylphenol) polysulfides during vulcanization of rubbers of the EPDM type. It has however encountered an undesirable effect concerning vulcanization kinetics. It in point of fact brings about an appreciable increase in the duration of the vulcanization reaction. Now, this duration is a critical parameter which governs productivity in the manufacture of articles made of rubber of the EPDM type for manufacturers of this sector.
Only a few sulfur-donor vulcanizing agents that do not present a risk relative to nitrosamines have been proposed for cross-linking elastomers of the EPDM type. Thus, mention may be made of compounds belonging to the dithiolactam family, such as dithiodicaprolactam, to the family of polythiophosphates, such as bis(O,O-2-ethylhexylthiophosphoryl polysulfide or to the family of polysulfide xanthates.
However, it is always desirable to widen the range of sulfur-donor vulcanizing agents that are provided in the field of the development of industrial rubbers (in particular EPDMs) so that specialists in this field can produce complex formulations that make it possible to achieve optimization of the mechanical properties required for vulcanizates, while obtaining a vulcanization time compatible with the productivity requirements of manufacturing units.